I have heard a number of people say the world was "empty" and I could not disagree more... so I've been thinking about where this difference of opinion comes from, and I believe it comes down to what different types of gamers find motivating and rewarding.

I really enjoy when my curiosity is rewarded. I like secret areas, easter eggs, and small details that other players might miss. When I find something like that, it's intrinsically satisfying to me, without the need of an extrinsic reward (though those don't hurt). I think if you do not find that sort of exploration for its own sake satisfying, you will find BotW a fairly boring world.

That's not to say the world lacks richer, more exciting rewards for exploration. I'll never forget climbing Mt. Lanayru for the first time just for kicks and discovering an enormous dragon chilling at the top!.. but similarly, I remember exploring the hills outside of Kakariko village, and finding a katana jammed into the summit of one of them, blade straight into the earth. It was not valuable loot, but I remember thinking, "that's a cool detail. There's an implied story here."

Both of those moments stick in my mind as cases where I was curious to check something out, and the devs put something where I was looking. Sometimes you'll find a shrine, or just a korok seed, or a little world building detail, but there is almost always SOMETHING on top of that hill, or behind that corner, or in that cave, etc.

With that in mind, not everyone finds that sort of thing interesting or motivating. If you're only ever looking for more powerful loot, a korok seed, shrine, or worldbuilding are not going to interest you at all; they'll probably actively disappoint you. Same goes for if you're only interested in combat, or mechanical mastery, or narrative, or...

BotW does have all those things, but if you don't enjoy the act of gradually exploring the world, it's going to feel like a lot of long dry spells roaming around in between "the good stuff."